Field of the Invention
This invention relates to an improved micropore open cell foam composite and a method for manufacturing the micropore open cell foam composites of the invention. The micropore open cell foam composites of the invention comprise a micropore open cell foam having an open cell content of greater than about 80% volume and an average pore size of about 200 microns or less and a phase change material in the open cell foam in the amount of 80% volume or greater.
Vaccines, antibiotics, and other temperature sensitive materials must typically be stored and transported under conditions wherein a narrow temperature range can be maintained for an extended period of time. Small size vacuum panel insulated refrigerators able to maintain a temperature of about 4xc2x0 C. may be used for storage of vaccines and antibiotics. Vacuum panel insulated shipping containers have been used to transport the temperature sensitive materials from the refrigerator storage location to the end use location which may be at remote sites. Therefore, the shipping box must be capable of maintaining the temperature sensitive materials at the desired temperature for an extended period of time.
Vacuum panel insulation alone is not sufficient to keep antibiotics, vaccines and other temperature sensitive materials within the critical range of temperature required for the duration of the transit time. Accordingly, shipping containers capable of maintaining the temperature over a narrow range for an extended period of time may utilize vacuum panel insulation in the walls of the container and a phase change material in the interior of the container.
Phase change material compositions store and release large quantities of energy, in melting and freezing, and are selected such that the phase change materials are capable of maintaining the temperature within the desired range.
In one method of storing and transporting temperature sensitive materials, such as vaccines, the materials are removed from a storage refrigerator, placed in a vacuum panel insulated shipping container and surrounded on all sides with packages of phase change material. There are a number of ways in which the phase change material can be contained to minimize or eliminate the problems of expansion and contraction associated with melting or freezing and, thereby, prevent any leakage of the phase change material, in a liquid state, through small opening or cracks in the packaging material. Examples of these methods include containment in phase change material/silica gels and dry powders, melt mixes of phase change materials/high-density polyethylene/ethylene/vinyl acetate copolymers/silica, in cross-linked pellets of high density polyethylene and imbibed into various porous substrates (e.g., plasterboard).
The prior art systems available are based on refrigerator systems that freeze water to provide thermal storage temperatures of 0xc2x0 C. or below. Exposure of temperature-sensitive medicinals such as vaccines, etc., to these low temperatures frequently results in irreversible damage due to freezing of water which is an essential component to many of these medicinal products. On the other hand, storage of the medicinals at temperatures greater than about 10xc2x0 C. can also cause irreversible damage to the medicinals.
The present invention is a micropore open cell foam composite comprising an open cell foam having an open cell content greater than 80% volume and an average pore size of about 1 to 200 microns and a phase change material wherein the phase change material is contained in the interstices of the micropore open cell foam in the amount of about 80% volume or greater. The micropore open cell foam composites of the present invention are useful in combination with insulating panels used in insulating various structures where it is desirable to maintain the interior temperature of the structure at a constant temperature plateau which is different from the temperature outside the structure. In one manifestation of the invention, the micropore open cell foam composites are employed in portable containers for storing and transporting temperature-sensitive materials such as medicinals, e.g. vaccines, antibiotics, etc., to remote locations which lack adequate means for providing conventional temperature control.
In another aspect of the invention, methods for manufacturing the micropore open cell foam composites are described. In accordance with one method of manufacturing the open cell foamed composites, the phase change material is imbibed at reduced pressure (vacuum) into the open pores of the micropore foam. Alternatively, elevated pressure imbibing can be substituted for the vacuum imbibing. Micropore open cell foam composites of the present invention are characterized by the ability to incorporate very high volumetric concentrations of phase change materials in the micropore open cell foams, up to greater than 80% by volume. Micropore open cell foam composites in accordance with the present invention can be subjected to repeated freezing and thawing cycles without xe2x80x9cooze outxe2x80x9d of the phase change material.
It is also possible to imbibe some materials by capillary attraction alone, without the application of either vacuum or pressure, into a hydrophilic micropore polyurethane open cell foam.
Micropore open cell foam composites in accordance with the present invention may contain relatively high volumetric concentrations of phase change material which can be particularly useful in applications where the available space is limited. The higher total loading of the phase change material possible with the micropore foam composites prepared in accordance with the present invention result in longer time-at-temperature (hold time) than with other methods of phase change material containment (e.g., PCM/silica gels or dry powders, or the melt mix of phase change material/high-density polyethylene/ethylene-vinyl acetate copolymer/silica).
In a particular embodiment of the invention, a micropore open cell foam composite is described which is particularly useful for use in a shipping container designed for transporting temperature-sensitive materials, such as antibiotics and vaccines. Many antibiotics and vaccines must be maintained within a critical range of temperature between 0 to 10xc2x0 C. Shipping containers constructed of vacuum panel insulation alone are unable to maintain these temperature sensitive materials within the critical range of temperature required. A micropore open cell foam composite in accordance with the present invention, comprising specific percentages of a linear crystalline alkyl hydrocarbon blend of C-14, C-15, and C-16 carbon chains, when used in conjunction with a vacuum panel insulated container, is capable of maintaining the temperature sensitive materials at approximately 6xc2x0 C. for an extended period of time. This particular phase change material blend, in sufficient quantity in the insulated shipping containing, has the necessary thermal storage capacity to keep the temperature sensitive material at a nearly constant temperature of about 6xc2x0 C. for 40 hours, or longer, in transit.